Cutting or welding by irradiating a material to be machined with laser light through a laser nozzle has been performed. In a case where the material to be machined is a steel plate, a carbon dioxide laser with a wavelength of 10.6 μm is typically used. Further, in recent years, layers having a wavelength of about 1/10 the wavelength of the carbon dioxide laser, such as a solid-state laser including a YAG laser, and a fiber laser have received attention as means for machining a steel plate.
Although most of the laser light radiated on a portion to be machined of the material to be machined is absorbed by the material to be machined and melts a base material, a part of the laser light is reflected from a surface of the material to be machined and a surface of a molten material. At this time, a reflecting direction of the laser light is not managed at all, and the laser light is reflected into every direction. For example, in a case where laser machining is laser cutting of the material to be machined, the laser light that has penetrated the material to be machined in a thickness direction is reflected from a support plate that supports the material to be machined and a bottom surface of a surface plate provided with the support plate.
Then, the reflected laser light is attenuated while again colliding with and being reflected from frames and the like that configure the laser machining device. However, a part of the reflected laser light is scattered around through a gap formed between the surface of the material to be machined and the laser machining device.
The laser light is harmful to the human body, and even the attenuated reflected light may harm people. Therefore, a safety standard including power density, maximum permissible exposure, and the like is set (JIS C6802). To meet the safety standard, covering the laser machining device with a cover has been performed.